1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus and an image forming method whereby a recording medium can be conveyed stably without affecting an image formed during conveyance on a curved surface.
Furthermore, the present invention also relates to a recording medium conveyance apparatus and a recording medium conveyance method, and more particularly, to a recording medium conveyance method and a recording medium conveyance apparatus whereby a recording medium can be conveyed stably by conveyance on a curved surface.
2. Description of the Related Art
In a system which conveys a recording medium on a conveyance body having curvature, such as a pressure drum, if an image is formed by an inkjet method, then it is necessary to convey the recording medium in a state of tight adherence to the surface of the conveyance body, without any floating up or wrinkling of the recording medium, in order that the recording medium does not contact the inkjet head.
In order to hold the recording medium tightly on the surface of a conveyance body, for example, Japanese Patent Application Publication No. 2008-179012 discloses an apparatus including a device which performs drying while conveying the recording medium suctioned on a rotating drum, in order to dry the ink on the recording medium after printing, reliably in a short time. However, if conveyance by suction is performed using a conveyance body having curvature, such as a rotating drum, then there are possibilities that density non-uniformities could be caused by ink liquid collecting at the suction holes when using thin paper, or the recording medium could not be suctioned onto the surface of the conveyance body due to floating up of the trailing end of the paper as a result of the high rigidity of the paper, when using thick paper.
Furthermore, if conveyance by suction is performed on a conveyance body having curvature such as a rotating drum, then there are possibilities that the recording medium cannot be suctioned in a state of uniform adherence to the surface of the conveyance body, due to slackness and cockling caused by permeation of the ink moisture content in the case of thin paper, and due to floating up of the trailing end of as a result of the high rigidity of the paper in the case of thick paper.
Furthermore, Japanese Patent Application Publication No. 2004-90490 describes a restricting device based on a roller, as an auxiliary device for a suctioning device. However, since the recording medium is restricted by making contact with a roller, then it has not been possible to apply such a device to a recording medium immediately after recording on which an image has been formed and has not yet dried. This is because the image could be transferred to the roller if the device is applied to such a recording medium immediately after recording.
Furthermore Japanese Patent Application Publication No. 2004-90490 describes an image recording apparatus including a suction position changing device which changes the suction position of a suctioning device in accordance with the movement of a roller. However, according to the apparatus disclosed in Japanese Patent Application Publication No. 2004-90490, processing is carried out on each individual wrinkle that occurs in the suctioned state, and if there is a plurality of wrinkles, then there is a possibility that the productivity declines dramatically. Furthermore, Japanese Patent Application Publication No. 2004-90490 does not provide a fundamental solution to the problem of suctioning the medium in a state of uniform adhesion to the surface of the conveyance body.
Japanese Patent Application Publication No. 2004-338175 discloses technology for altering the suction air flow volume in accordance with the type (rigidity, thickness) of recording medium, and describes an inkjet recording apparatus which suppresses decline in the temperature of the recording medium, by altering the suction air flow volume in accordance with the type (rigidity, thickness) of the recording medium.
Japanese Patent Application Publication No. 2003-211652 and Japanese Patent Application Publication No. 10-193772 describe a printing apparatus and a printing method in which a non-contact type of paper restricting device for pressing the recording medium against the surface of the medium is provided, and a printing apparatus and a printing method in which a recording medium is pressed against a conveyance device by an air blowing device.
Even if the suction air flow volume is simply controlled or an air blowing device is simply provided, however, it is difficult to tightly hold and convey the whole of a sheet of thick paper on the surface of a conveyance body having curvature. Furthermore, it is possible to apply the required suction pressure to a recording medium which is thick paper and convey the medium by suction in a state where the thick paper is forcibly caused to adhere tightly to the pressure drum by increasing the pressure of the blown air flow, but if air of a high flow pressure, such as compressed air, is directed onto an image immediately after recording, then the image which is in a liquid state is caused to flow on the recording medium, and hence there is a possibility that image quality is impaired.
Moreover, even if the suction air flow volume is simply controlled or an air blowing device is simply provided, then it is difficult to correct cases where a thin paper is suctioned in a slack state, and if the air blowing timing and suction timing are not appropriate, then there is a concern that the paper will be suctioned in a disorderly fashion.